The present invention relates to a valve resting mechanism for a multi-cylinder engine. More particularly, the invention relates to a valve resting mechanism for a cylinder control type engine, for retaining a proper running state for an engine load by resting the multiple cylinders partially according to the acting state of the engine.
Most of multi-cylinder engines of the prior art are run by feeding the fuel and air individually homogeneously to all the cylinders according to a load all over drive ranges because they are restricted on the mechanism of a valve actuating system.
In the valve actuating mechanism capable of performing a drive resting the cylinders partially or changing the valve timing, on the other hand, there is known (see for example Japanese patent application Kokai publications No. 6-299828 and No. 7-49016) a valve actuating mechanism for the engine to make it easy to return from the partially rested run to the run with all the cylinders being active or to change the valve timing.
In the multi-cylinder engine of the type in which the fuel and air are fed individually homogeneously to all the cylinders in accordance with the load all over the drive ranges, however, the combustion efficiency at an idling time or at a low speed/under a low load is generally so poor as to increase the pumping loss thereby to raise a problem that the thermal efficiency is lowered. On the other hand, the valve actuating mechanism of the engine, as disclosed in Japanese patent application Kokai publication No. 6-299828, has such a complicated mechanism as to raise another problem that its assembly and control are troublesome.
An object of the invention is to solve the above-specified problems and to provide a valve resting mechanism for a cylinder control type engine, which can improve the combustion efficiency at the idling time and at the low speed/under the low load and can simplify the valve actuating mechanism of the engine.
In an overhead cam engine comprising: a cylinder head fixed on a cylinder block having multiple cylinders; an intake/exhaust valve for opening/closing an intake/exhaust port formed in the cylinder head; and a cam type valve actuating mechanism disposed over the cylinder head for actuating the intake/exhaust valve for the opening/closing actions, the cam type valve actuating mechanism including: a cam formed on a camshaft made rotatable according to the rotation of the engine; and a rocker arm adapted to rock on a rocker arm shaft in accordance with the rotation of the cam, for giving the opening/closing actions to the intake/exhaust valve, according to an aspect of the invention, there is provided a valve resting mechanism for a cylinder control type engine, wherein the improvement resides: in that the rocker arm includes a first rocker arm and a second rocker arm for rocking independently of each other on the rocker arm shaft, the first rocker arm being adapted to rock when given the rotational motion of the cam, the second rocker arm being adapted to give the opening/closing actions to the intake/exhaust valve; in that the first and second rocker arms have individual engagement portions, with which a pin to be slidably moved by an electromagnetic drive device comes into engagement; and in that the rocking motion is transmitted from the first rocker arm to the second rocker arm in the engaged state where the pin is engaged by both the engagement portions whereas the rocking motion is not transmitted from the first rocker arm to the second rocker arm in the disengaged state where the pin is not engaged by the engagement portion of the second rocker arm.
One of the engagement portions formed on the first and second rocker arms is formed at the boss portion of the first rocker arm by a pin guide hole for guiding the pin slidably, whereas the other engagement portion is formed at the boss portion of the second rocker arm by an engagement hole to be engaged by the pin. Moreover, the pin is inserted at all times into the pin guide hole of the first rocker arm and is biased in a direction to come out of the engagement hole of the second rocker arm by a return spring which is arranged between the head of the pin and the boss portion.
The electromagnetic drive device includes: a movable element for sliding the pin in the axial direction; a stator for establishing an electromagnet; and a clearance between the movable element and the stator for regulating the sliding extent of the movable element in the axial direction.
The sliding stroke of the pin is controlled by the sliding extent of the movable element. The pin and the movable element are mutually slidable toward the center of the rocking fulcrum of the rocker arm from the sliding faces of the engagement portions. On the other hand, the pin rocks while engaging at all times with the engagement portion of the first rocker arm and is brought by the sliding motion of the movable element into rocking engagement with the engagement portions of both the first and second rocker arms.
The first rocker arm and the second rocker arm are provided with return springs so that they may rock while following the motions of the cam and the intake/exhaust valve at all times.
In this cylinder control type engine, valve resting mechanisms are provided separately to separate cylinders so that they can operate independently for separate cylinders, and the engagement or disengagement of the such mechanisms with or from the first rocker arm and the second rocker arm provided to each cylinder are controlled mechanism by mechanism according to the running state of the engine.
The stator of the electromagnetic drive device includes: a case fixed on the cylinder head through a bracket; a yoke arranged in the case; and an exciting coil arranged in the yoke. On the other hand, the electromagnetic drive device includes a permanent magnet midway of the iron core for forming a magnetic path so that the movable element may be self-retained.
With the valve resting mechanism for the cylinder control type engine being thus constructed, when the electromagnetic drive device is activated in response to the high speed/the high load of the engine, the pin slides and moves so that the first and second rocker arms can be connected to each other to open/close the intake/exhaust valve.
When the electromagnetic drive device for the cylinder selected is inactivated, on the other hand, the pin of the corresponding cylinder is returned to the initial position by the return spring so that the first and second rocker arms come into the disconnected state. Then, even if the first rocker arm rocks according to the rotation of the cam, the second rocker arm does not rock to rest the selected cylinder.
Therefore, this valve resting mechanism for the cylinder control type engine can control the valve drive and the valve rest simply with or without the drive of the electromagnetic drive device so that the responding speed of the drive control is better improved than that of the hydraulic valve resting mechanism of the prior art.
At the idling time or at the low speed/under the low load, moreover, the valve drive is partially inactivated to rest the cylinders partially so that the engine can be run with a proper number of cylinders to improve the combustion efficiency. According to the invention, therefore, the pumping loss can be lowered to improve the thermal efficiency. In this valve resting mechanism for the cylinder control type engine, moreover, the intake valve and the exhaust valve can be assembled and controlled separately for the individual cylinders so that they can cope with the various cylinder controls.